Everyday the Sun pours down onto the Earth a vast quantity of radiant energy many many times greater than the total now used by Man. Some of this energy, together with carbon dioxide and water, Nature traps in trees and other plants by conversion into giant chemical molecules, collectively called biomass. The major components (about 60% to 80%) of this mixture are polysaccharides. These are long and substantially linear chains, the individual links of which are simple sugars. The remaining component (about 15% to 25%) is called lignin and is a complex network of joined aromatic rings of the type present in liquid diesel engine fuel. The energy trapped within plants can be recovered, in part, by breaking down the long chains into their constituent sugar links for subsequent standard fermentation into bioethanol. In contrast, the breakdown of the lignin network can yield simple aromatic compounds for possible direct incorporation into diesel fuel. The problem facing chemical engineers has been how to achieve these demonstrated chemical breakdowns on a large-scale, commercially practical, and energy efficient way.
There exists immense amounts of biomass materials in forests and crops, and cellulose, the main component, is one of the most abundant natural resources available on the Earth. In this regard, natural cellulosic feedstocks are now commonly referred to as “biomass,” and biomass materials are known to generally consist primarily of cellulose (˜40% to ˜50%), hemicellulose (˜20% to ˜30%), and lignin (˜15% to ˜25%) bound together in a complex structure together with smaller amounts of pectins, proteins, and ash. Many types of biomass, including, for example, wood, paper, agricultural residues such as bagasse, switchgrass, wheat or sorghum straw, corn husks, and the like have long been considered as possible feedstocks for the manufacture of certain organic chemicals, but thus far existing biomass conversion technologies have achieved only limited success. It is believed by many that due to the complex chemical structure of most biomass materials, microorganisms and enzymes cannot effectively attack the cellulose component without prior treatment. Indeed, conventional methods for converting cellulose to glucose by way of acid hydrolysis and enzymatic saccharification are known to be inefficient and, consequently, are not yet commercially viable.
More recently, however, the chemical conversion of cellulose with supercritical water to obtain various sugars has been studied. (see, e.g., M. Sasaki, B. Kabyemela, R. Malaluan, S. Hirose, N. Takeda, T. Adschiri & K. Arai, Cellulose hydrolysis in subcritical and supercritical water, J. Supercritical Fluids, 13, 261-268 (1998); S. Saki & T. Ueno, Chemical conversion of various celluloses to glucose and its derivatives in supercritical water, Cellulose, 6, 177-191 (1999).) These more recent studies are among the first to demonstrate that cellulose may be rapidly hydrolyzed in supercritical water to yield glucose (in high yield) in either flow or batch type micro-reactors. The use of flow or batch type micro-reactors, however, is not a realistic option for the commercial-scale production of cellulosic based motor fuels.
Nowadays, everyone is aware of the desirability of having new domestic sources of liquid fuels for diesel as well as gasoline engines. Likewise, it is generally recognized that the USA has been living in the Age of Plastics for the past 75 years. This has become a throwaway age and multi-ton quantities of plastics are discarded daily all around the world.
In the major cities of the USA, it is now standard to have special bins everywhere in which recyclable material can be dumped. Originally this recyclable designation was restricted to paper and cardboard but now plastics in general are accepted. Strangely enough, in Seattle polystyrene foam and packaging material is excluded, and must be dumped in the regular garbage cans. The contents of the recycle bins are collected in a special truck and are transported to a municipal recycling center. There the various components are separated.
Now the discarded plastics, separated at the recycle center, consist of long chains of thousands of atoms called polymers. Of the commercially most important polymers, polystyrene (PS), polyethylene (PE) and polypropylene (PP), have chains that contain only carbon and hydrogen atoms in amounts similar to the hydrocarbons in diesel and gasoline fuels. Thus, the molecules in diesel and gasoline are chemically similar to the polymers but are much smaller in size. It has therefore been appreciated for some time that if the long chains of the plastics could be broken down into smaller pieces these moieties could find use as chemical feedstocks.
One of the most intriguing and environmentally sound approaches to breaking down plastics is simply to use water alone, heated to its supercritical state. About a decade ago this chemical-free technology was comprehensively discussed in an English language review by P. E. Savage (Chem. Rev. 1999, 99, 609). Since then few modern review have appeared. However, numerous articles, mostly from Japan and China, have appeared each year dealing with the treatment of plastics with supercritical water. All of these publications emphasize that when water is heated to 374.4 C or above, the pressure concomitantly generated is 217.7 atm and the water then becomes a powerful new reactive solvent. Temperatures above 400 C seem to make the water even more effective in its new role. For example, it now dissolves PS and breaks it down in 100% yield into a mixture of styrene, methylstyrene, styrene dimers and trimers, toluene, ethylbenzene, isopropylbenzene, 1,3-diphenylpropane and 1,3-diphenylbutane. (H. Kwak, H.-Y. Shin, S.-Y. Bae and H. Kumazawa, J. Appl. Poly. Sci. 2006, 101, 675). All of these substances are immiscible with water at room temperature and could be components of a diesel fuel.
These and numerous other similar reactions (J. A. Onwudili & P. T. Williams, Chemosphere 2009, 74(6), 787) demonstrate clearly that plastics can be broken down by treatment with supercritical water. Apparently the water and plastic undergoes the water gas reaction and hydrogen is released to combine with the chain fragments from the plastics. This has actually been demonstrated by the use of deuterium oxide in place of water and the consequent finding of deuterium in the fragments. However, since nearly all water-plastic reactions have been run in a batch mode on a very small scale, the chemistry so elegantly elucidated does not provide answers to the questions necessary for the future development of a commercially-sized, practical, continuous, supercritical water-based process.
As is commonly understand by those with backgrounds in chemical engineering, petroleum-based diesel fuels are produced from the fractional distillation of crude oil between 200° C. (392° F.) and 350° C. (662° F.) at atmospheric pressure, resulting in a mixture of carbon chains that typically contain between 8 and 21 carbon atoms per molecule. Diesel fuels are approximately similar to fuel oils used for heating (fuel oils no. 1, no. 2, and no. 4). All fuel oils consist of complex mixtures of aliphatic and aromatic hydrocarbons. The aliphatic alkanes (paraffins) and cycloalkanes (naphthenes) are hydrogen saturated and compose approximately 80-90% of the fuel oils. Aromatics (e.g., benzene) and olefins (e.g., styrene and indene) compose 10-20% and 1%, respectively, of the fuel oils. Fuel oil no. 1 (straightrun kerosene) is a light distillate which consists primarily of hydrocarbons in the C9-C16 range; fuel oil no. 2 is a heavier, usually blended, distillate with hydrocarbons in the C11-C20 range. Straight-run distillates may also be used to produce fuel oil no. 1 and diesel fuel oil no. 1. Diesel fuel no. 1 and no. 2 are similar in chemical composition to fuel oil no. 1 and fuel oil no. 2, respectively, with the exception of the additives. Diesel fuels predominantly contain a mixture of C10 through C19 hydrocarbons, which include approximately 64% aliphatic hydrocarbons, 1-2% olefinic hydrocarbons, and 35% aromatic hydrocarbons.
Accordingly, and although some progress has made with respect to the development of biomass and/or waste plastic conversion systems, there is still a need in the art for new and improved machines, systems, and methods for converting biomass and/or waste plastics into simple sugars, hydrocarbons, and aromatic chemicals which, in turn, can be readily converted into liquid transportation fuels. The present invention fulfills these needs and provides for further related advantages.